The present invention relates to a ribbon feed device for typewriters and other office machines, wherein the ribbon is carried in a cartridge and is caused to advance longitudinally past the printing point by a feed mechanism.
In a known ribbon feed device, the ribbon is carried by a cartridge in which ribbon-carrying spools rotate. For facilitating the insertion of the ribbon in a printing unit of the kind having a single type-bearing head, a control lever is provided which raises a ribbon-guiding fork above the printing point, thus making it easy to mount the cartridge in the unit. A ribbon feed mechanism then provides for the longitudinal movement of the ribbon past the striking point.
In the case where the printing ribbon is of the inked type, the use of a movement reversing mechanism is required. In a mechanism of known type, the mounting of the cartridge does not require the actuation of any other part of the movement reversing mechanism. In fact, a pair of sensing elements are pivoted within the driving spindles of the spools and, through apertures in the spindles and the spools, sense the presence of the wound ribbon from the inside. Each sensor then commands the reversal of the movement of the ribbon when the number of the turns of wound ribbon is no longer sufficient to keep the sensor concerned inoperative. The use of sensors of this type, however, makes the ribbon movement reversing mechanism itself rather complicated and costly to construct.
In the case where the printing ribbon is of the carbon coated type, the ribbon is fed through unidirectionally, once only, before the cartridge is changed. In one such device, the feed of the ribbon is carried out by a driving roller which, during the replacement of the cartridge, is held away from the ribbon by means of a control lever. It is therefore necessary to act on two separate members, one of which provides for the raising of the ribbon fork and the other for the control of the feed mechanism.